This invention relates to opaque molded articles of polymerizable molding compositions, containing unsaturated polyesters and copolymerizable monomers, as well as conventional catalysts and additives.
The invention furthermore relates to opaque coatings of coating materials based upon unsaturated polyesters and copolymerizable monomers containing conventional catalysts and additives.
The invention relates also to a process of producing the opaque molded articles and opaque coatings.
Finally, the invention is concerned with materials having opaque, white or colored synthetic resin surfaces.
The term "coating materials" is understood to mean in this disclosure all liquid forms of preparations required for the production of coatings, laminates, varnish structures, such as fillers, primers, size varnishes, top coats, casting and molding compounds, and the like.
The term "coatings" is to mean herein all layers, coatings, laminates, or varnish coats obtained from the aforementioned coating materials.
The term "materials" is to mean in this text all materials suitable for synthetic resin coatings of wood, wood materials, pressed materials, cardboard, paper, glass, fabric, or metal. Wood materials are understood to mean finished wood products, such as fiberboards, hardboards, jointed boards with and without veneer. Pressed materials are laminated materials from papers, fabrics, fibrous fleeces, or glass mats, impregnated with synthetic resins, cured with the use of pressure and heat. Also plastics can in certain cases serve as "materials" for synthetic resin coatings. Although the materials need not have a planar shape, panels or plates are preferably provided. The term "materials" also includes those above-mentioned substances which had been subjected to a pretreatment. Thus, wood and wood materials can be stained, metals can be provided with a wash primer, a phosphate coating, or a chromate coating. Furthermore, the materials can be sized, primed, or coated with an adhesive or varnish layer.
The term "polymerizable molding compositions" includes all molding compounds technically employed based upon unsaturated polyesters and copolymerizable monomers with the use of conventional catalysts, accelerators, additives, and customary curing processes. Such polyester molding compositions have attained great significance in technology. Insofar as the production of coatings is concerned, these polyester molding compositions are called "polyester coating materials" in the following description. The voluminous literature concerned with the composition, utilization, and technology of polyester molding compositions or polyester coating materials is summarized, inter alia, in the standard works "Polyesters and Their Applications" (Bjorksten, Tovey, Harker, and Henning, Hew York, Reinhold Publishing Corporation, 1956), "Polyester Resins" (Lawrence, New York, Reinhold Publishing Corporation, 1960), and "Unsaturated Polyesters: Structure and Properties" (Boenig, Amsterdam, Elsevier Publishing Company, 1964).
The curing of polyester molding compositions and of coatings made from polyester coating materials can be effected in various ways. This process can be conducted without external heat supply at ordinary room temperatures, if the molding compositions or coating materials contain peroxides as curing agents and suitable accelerators. The curing agents and accelerators, however, must be adapted to each other.
The curing process initiated by peroxides can be further accelerated by supplying external heat or by irradiation with infrared rays, or by the use of high frequency energy.
In this manner, transparent molded articles have heretofore been obtained from transparent or translucent molding compositions. In contrast thereto, opaque molded articles have previously been produced only from pigmented molding compositions, i.e. those to which have been added hiding pigments, such as for example, titanium dioxide, carbon black, iron oxide, dyes, etc. These opaque molded articles possess a more or less high residual transparency, dependent on the content of hiding pigments.
Another way of curing polyester molding compositions and coatings prepared from polyester coating materials is irradiation with ultraviolet light. In this case, the peroxide curing agent and the accelerator can, in principle, be omitted. In place thereof a photo-chemically active sensitizer is employed. The latter effects, under the action of UV light, a splitting off of radicals, which initiates a polymerization of the entire polyester layer. The UV rays employed in this process are normally produced by high pressure mercury vapor lamps or low pressure mercury vapor lamps or superactinic fluorescent tubes. In place of ultraviolet light, it is also possible to employ sunlight or another, more strongly ionizing radiation, for curing purposes.
When UV light is used for curing, it has heretofore been possible to cure only transparent molding compositions to transparent molded articles or transparent coatings, in contrast to the curing process initiated by peroxides and suitable accelerators. The conventional UV curing processes are summarized in the articles "Die Lichthaertung von Polyester-Lacken" [Light Radiation Curing of Polyester Resin Varnishes] (Eugen Richter, "Moderne Holzverarbeitung" [Modern Wood Processing], Vol. 10, 1968, pp. 604-606) and "Lackhaertung durch Ultraviolettes Licht" [Varnish Curing by Ultraviolet Light], (Dr. Wolfgang Deninger and Dr. Manfred Patheiger, "Industrie-Lackier-Betrieb" [Industry Varnishing Operation], 37th year, Vol. 3, March 1969, pp. 85-91).